3:40 PM Abstract No. 47 Characterization of in vivo ablation zones following percutaneous pulmonary cryoablation: expected and experimental findings

Abstract

To determine the in vivo ablation zone when treating pulmonary tumors with cryoablation, with attention to differences in probe type, probe number, and anatomical factors. CT imaging was reviewed retrospectively following cryoablation of lung tumors using Galil Medical cryoprobes with a triple freeze protocol. Postprocedure volume of the ablation zone was calculated by measuring the maximum axial diameter (2a) and 90° orthogonal diameters (2b and 2c), and applying the formula for volume of an ellipsoid: 4/3*πabc. Statistical comparison was calculated using a student’s t-test or 1-way ANOVA. Linear regression was used to model ablation size with respect to probe number or distance to pleura or vessel. Graphical plots were created using the equation for an ellipse: x2/a2+y2/b2 = 1. Mean volume of in vivo lung ablation with a single 17-gauge cryoprobe measured 3.0 cm3(95% CI [2.3, 3.6], n = 15), a significant difference compared to the manufacturer published -40°C isotherm volume of 7.1 cm3 in room temperature gel (p<0.001). Mean ablation volume of a larger 13-gauge cryoprobe was 4.3 cm3 (95% CI [1.7, 6.9], n = 2), which was not significantly different compared to the smaller 17-gauge probe (p = 0.22). Mean cryoablation zone was not significantly affected by nodule distance to the pleura (p = 0.54) or distance to a vessel larger than 3 mm in diameter (p = 0.55). Ablation volume was significantly increased (p<0.001) with the use of multiple cryoprobes, at a rate of 10.8 cm3 increase per additional probe (2 probes: 12.9 cm3, 95% CI [8.2, 17.6], n = 24; 3 probes: 25.3 cm3, 95% CI [8.0, 42.6], n = 5). The increased ablation zone size with multiple probes was more attributable to increased short axis length (9.6 mm increase per probe) compared to the long axis (5.6 mm increase per probe). The in vivo effective ablation zone differs significantly from manufacturer supplied specifications in pulmonary cryoablation. Ablation zone volume is increased by utilizing more cryoprobes, but not affected by cryoprobe gauge or proximity to pleura or vessel.